1. Field of Invention
This invention relates to a toners within a set of toners used in developing a color image, and a method of making the toners, which toners are made to have a matching melt flow index (MFI) value.
2. Description of Related Art
Historically, xerography has not been required to deliver prints of the same caliber as offset lithography. The offset lithography customer demands a level of print quality much higher than is available from conventional xerographic machines.
U.S. Pat. No. 5,545,501 describes an electrostatographic developer composition comprising carrier particles and toner particles with a toner particle size distribution having a volume average particle size (T) such that 4 xcexcm less than T less than 12 xcexcm and an average charge (absolute value) pro diameter in femtocoulomb/10 xcexcm (CT) after triboelectric contact with said carrier particles such that 1 fC/10 xcexcm less than CT less than 10 fC/10 xcexcm characterized in that (i) said carrier particles have a saturation magnetization value, Msat, expressed in Tesla (T) such that Msat greater than 0.30 T, (ii) said carrier particles have a volume average particle size (Cavg) such that 30 xcexcm  less than Cavg less than 60 xcexcm, (iii) said volume based particle size distribution of said carrier particles has at least 90% of the particles having a particle diameter C such that 0.5 Cavg less than C less than 2 Cavg, (iv) said volume based particles size distribution of said carrier particles comprises less than b % particles smaller than 25 xcexcm wherein b=0.35 X (Msat)2 X P with Msat saturation magnetization value, Msat, expressed in T and P: the maximal field strength of the magnetic developing pole expressed in kA/m, and (v) said carrier particles comprise a core particle coated with a resin coating in an amount (RC) such that 0.2% w/w less than RC less than 2% w/w. See the Abstract. Melt flow index properties and the need for matching such properties among different toners of a set of toners are not described.
Co-pending U.S. patent applications Nos. 09/520,439 pending; 09/520,437 (now U.S. Pat. No. 6,242,145) and 09/520,359 allowed, all filed Mar. 7, 2000, and each incorporated by reference herein in its entirety, describe toners and developers for particular use in devices utilizing hybrid scavengeless development, the toners including toner particles of at least one binder, at least one colorant, and optionally one or more additives, the toner exhibiting a charge per particle diameter (Q/D) of from xe2x88x920.1 to xe2x88x921.0 fC/xcexcm with a variation during development of from 0 to 0.25 fC/xcexcm and the distribution is substantially unimodal and possesses a peak width of less than 0.5 fC/xcexcm, and the toner has a triboelectric charge of from xe2x88x9225 to xe2x88x9270 xcexcC/g with a variation during development of from 0 to 15 xcexcC/g following triboelectric contact with carrier particles. The developer of a mixture of carrier particles and the toner particles has a triboelectric value of from xe2x88x9235 to xe2x88x9260 xcexcC/g, a charge distribution (Q/D) of from xe2x88x920.5 to xe2x88x921.0 fC/xcexcm and the distribution is substantially unimodal and possesses a peak width of less than 0.5 fC/xcexcm, preferably less than 0.3 fC/xcexcm, and a conductivity of the developer ranges from 1xc3x9710xe2x88x9211 to 10xc3x9710xe2x88x9215 mho/cm as measured at 30 V. The method of forming the toner having controlled properties includes feeding at least one binder and at least one colorant into a mixing device at a feed ratio, upon exit of the mixture from the mixing device, monitoring one or more properties of the mixture with at least one monitoring device, wherein if the monitoring indicates that the one or more properties being monitored is out of specification, removing the monitored mixture from the method and adjusting the feed ratio by adjusting the feeding of the at least one binder or of the at least one colorant, thereby retaining in specification mixture in the method, grinding the in-specification mixture, optionally together with a portion of one or more external additives to be added to the mixture, classifying the ground in-specification mixture, and mixing the classified in-specification mixture with one or more external additives to obtain the toner having controlled properties.
While these co-pending applications describe a range of rheology or MFI for a single toner, no required relationship of such properties among a set of toners is described.
Co-pending U.S. patent application No. 09/520,360, filed Mar. 7, 2000 and incorporated by reference herein in its entirety, describes a toner and developer for use in an imaging system employing a magnetic brush developer unit. The toner contains at least one binder, at least one colorant, and preferably one or more external additives of one or more of silicon dioxide powder, untreated titanium dioxide powder and zinc stearate (in amounts of at least 0.1 percent by weight of the toner). The toner particles, following triboelectric contact with carrier particles, exhibit a charge per particle diameter (Q/D) of from 0.6 to 0.9 fC/xcexcm and a triboelectric charge of from xe2x88x9220 to xe2x88x9225 xcexcC/g. The toner particles preferably have an average particle diameter of from 7.8 to 8.3 microns. The toner is combined with carrier particles to achieve a developer, the carrier particles preferably having an average diameter of from 45 to 55 microns and including a core of ferrite substantially free of copper and zinc coated with a coating comprising a polyvinylidenefluoride polymer or copolymer and a polymethyl methacrylate polymer or copolymer.
What is still desired is a set of toners and developers that have excellent overall print quality, particularly with respect to gloss within and among the different colors of the developers and toners, and a method of making such toners.
It is an object of the present invention to provide a set of toners for developing a color image in which at least three, and preferably four, of the toners from the set each have substantially the same melt flow index property such that the developers containing such toners can achieve xerographically produced images having excellent gloss, color and image quality.
It is a further object of the invention to develop such toners and developers capable of producing such high quality color images when used in a development device that utilizes either a radiant fusing system or a roll fusing system.
It is a still further object of the invention to provide a method for manufacturing the toners and developers to consistently achieve the desired melt flow index value.
These and other objects of the present invention are achieved herein, where the invention relates to at least three, and preferably four, differently colored toners for use in developing a color image in the same image developing device, wherein each of the at least three differently colored toners comprises at least one binder and at least one colorant, and has substantially the same melt flow index value.
The toners are produced by individually producing each toner of the set so as to have substantially the same melt flow index value in a method comprised of:
(i) forming a toner by feeding at least one binder and at least one colorant into a mixing device to form a mixture,
(ii) upon exit of the mixture from the mixing device, measuring a rheology property of the mixture with at least one monitoring device, and comparing the measured rheology property to a target property range that the measured rheology property must be within in order for the toner to achieve the desired melt flow index value, wherein if the measuring indicates that the rheology property is outside of the target property range, feed amounts of the at least one binder or of the at least one colorant into the mixing device are adjusted,
(iii) grinding the mixture, optionally together with a portion of one or more external additives to be added to the mixture,
(iv) classifying the ground mixture,
(v) mixing the classified mixture with one or more external surface additives to obtain the toner having the desired melt flow index value, and
(vi) repeating steps (i) to (v) for each additional differently colored toner desired to have the melt flow index value, thereby achieving at least three differently colored toners having substantially the same desired melt flow index value.